Element 11 on the periodic table is Sodium (Na), derived from the Latin word natrium. Its atomic number is 11, signifying the number of protons in its nucleus. Sodium is a highly reactive alkali metal. In its ionic form, it is one of the most abundant elements on Earth and serves as an essential nutrient necessary for the biological function of nearly all living organisms.
Defining Sodium: Atomic Structure and Chemical Properties
Sodium belongs to Group 1 of the periodic table, placing it among the alkali metals known for their high reactivity. A sodium atom features 11 protons and 11 electrons, arranged in a shell structure of 2, 8, and 1. This configuration means it possesses a single valence electron in its outermost shell.
This lone valence electron is loosely held, which is the primary reason for sodium’s high chemical reactivity. The atom readily loses this electron to achieve a stable outer shell, forming a positively charged ion, Na+. This tendency means elemental sodium is almost never found uncombined in nature. In its pure state, sodium is a soft, silvery-white metal that can easily be cut with a knife. The metal reacts violently and exothermically with water, immediately releasing hydrogen gas and forming sodium hydroxide.
Natural Occurrence and Industrial Production
Due to its extreme reactivity, elemental sodium metal does not naturally exist on Earth; it is always found chemically bound in compounds. Sodium is the sixth most abundant element in the Earth’s crust, accounting for approximately 2.6% of its composition by mass. Its most common compound is sodium chloride (table salt), found in massive quantities in seawater and large underground salt deposits.
Sodium compounds are also found in various mineral forms, such as trona, a type of sodium carbonate mineral. To obtain pure sodium metal for industrial uses, it must be separated from its compounds using a specialized, energy-intensive process. The primary commercial production method is the electrolysis of molten sodium chloride, often carried out in a Downs cell. This process uses an electric current to break the strong chemical bonds in the salt, yielding pure sodium metal and chlorine gas.
The Critical Biological Role
In the human body, sodium is the most abundant positively charged ion (cation) in the extracellular fluid. Its primary physiological function is to maintain fluid and blood pressure balance through osmosis, where water follows the concentration gradient of sodium ions. This regulation is crucial for maintaining total blood volume and overall fluid balance.
Sodium ions are also indispensable for the proper functioning of nerve and muscle cells. Nerve impulse transmission relies on the rapid influx of sodium ions across the neuron membrane, creating an electrical signal known as an action potential. Furthermore, a specialized protein complex called the sodium-potassium pump, found in the cell membranes, actively transports three sodium ions out of the cell for every two potassium ions it brings in. This continuous, energy-consuming process maintains the necessary concentration gradient that drives nerve signaling and helps regulate cell volume.
A healthy intake of sodium is necessary to support these functions. The minimum physiological requirement for an adult is around 500 milligrams per day. However, a high dietary intake, often far exceeding this requirement, is a well-established risk factor for elevated blood pressure (hypertension). Conversely, a severe deficiency, known as hyponatremia, can lead to symptoms like confusion, seizures, and coma due to the disruption of fluid balance within the cells.